1. Field of the Invention
This invention relates generally to the mass-production of medical tablets. More particularly, the invention relates to an apparatus for mass-producing medical tablets wherein interfacial friction between the tablet and the die and punch is prevented whereby problems and difficulties due to interfacial friction, such as capping, lamination and binding, are avoided to ensure a trouble-free molding operation.
2. Description of the Prior Art
It is known in the art that when a powdery or granular material is molded into tablets under heavy load, interfacial friction occurs between the tablets and the punches, and between the tablets and the walls of die cavities. This friction tends to cause various troubles, such as capping, lamination and adhesion, and interrupt the molding operation. In order to avoid these troubles, the common practice is to admix a lubricant with the medicine, and to mold the admixture into tablets. However, the lubricant content is likely to make the tablets fragile, and retard the dissolution rate and/or the disintegration rate of the tablets in the gastric juices. These are fatal defects for medicine.
In essence, a lubricant has only to exist interfacially between the tablets and the dies, wherein its quantity need not be large. At laboratories a lubricant is actually coated by hand on the surfaces of punches and dies, and this practice is found satisfactory. Nevertheless, there are many difficulties in putting this method into industrial practice. In order to improve the situation many proposals have so far been made, some of which are enumerated below:
Japanese Patent Publication No. 41-11273 (1966) discloses a method of spraying a solution or dispersion of a lubricant, onto the surfaces of punches and dies. This method entails a difficulty in selecting an appropriate solvent, and furthermore, it will be of particular disadvantage when a rotary type of tableting machine is employed, in which the spray application must be intermittent and instantaneous so as to be accurately timed with the movement of the punches. In addition, as the rotating speed of the turntable increases, the intervals of spraying must be accordingly short. However, when the rotating speed exceeds a certain limit, it happens that the lubricant droplets fail to reach the top portions of lower punches.
Japanese Patent Publication No. 48-20103 (1973) discloses a method of blowing an air jet containing a dispersed lubricant onto the punches and dies. However, it is extremely difficult to disperse a small amount of lubricant in air, and in general, since the air is a compressible fluid, it is difficult to secure an instantaneous spray intermittently so as to be in timing with the movement of the punches.
U.S. Pat. No. 3,626,043 discloses a method consisting essentially of two stages; firstly, to compress a lubricant per se in a press die, and secondly, to use the same die in which the lubricant film remains on the surfaces after the mold is removed. In this method a double molding is required, which calls for a tableting machine of a double compression type. But this type of tableting machine is large-sized, and the working efficiency will be lower than that of a single compression type because of the reduction in the rotating speed of the turntable which undergoes an increased centrifugal force in accordance with an increase in its diameter. Another disadvantage is that the thickness of the lubricant film is previously determined by the clearance between the punch and the die, thereby making it impossible to control it as desired.
The present invention is directed toward solving the problems encountered with respect to the prior art described above. The object of the invention to provide an improved apparatus for mass-producing medical tablets in which a lubricant is automatically applied to the surfaces of the punches and dies. The lubricant is not allowed to be contained in the molded tablets, and the desired weight of the molded tablets is maintained irrespective of the application of a lubricant.
Another object of the present invention is to provide an improved tableting apparatus which is relatively simple in construction but which ensures a high tableting ability.
Other objects and advantages will become more apparent from the following description when taken in connection with the accompanying drawings.